Competition authorities and litigants worldwide have increased the use of economic quantitative methods and economic expert witnesses as a means to produce and support evidence in merger and antitrust cases. The application of quantitative techniques to antitrust has arisen naturally from the need to answer the central questions of antitrust analysis, such as, market definition and market structure issues, analysis of pricing and non-pricing behaviour by firms, quantification of damages and efficiencies and dynamic issues of entry and product reallocation. The paper aims, on the one hand, to briefly describe the main aspects of the most commonly used quantitative techniques in antitrust analysis, and on the other hand, to quantify their use in EU merger and antitrust decisions from 2004 until 2011. Moreover, we also codify the Commission‘s opinion on the techniques utilized. The paper then explores the substantive law framework for the assessment and evaluation of this quantitative evidence in EU competition law by the European Commission and the Courts, in particular topics relating to the standard of proof and evidential cogency and the interaction between the different concepts of causation in law and econometrics, whereas Section 5 provides a unique empirical analysis of the probative value of different kinds of econometric evidence, by performing for the first time a quantitative analysis of the opinion of the European Commission for the particular techniques used and their average evidential weight.